A measuring device for a machine tool is known in which a sensor is mounted on a movable support which is attached to a slidable carriage.
The sensor on the carriage and/or tool holding and positioning mechanism of the machine tool can be employed for measurements of the workpiece. This sensor travels along and contacts the workpiece after starting from a calibrating position. From the direct displacement of the carriage, a calculator can give the radius of a workpiece clamped in the chuck or of a shaft which is held between the headstock and the tailstock.
Such measurement of the workpiece radius is no longer sufficiently accurate in view of today's exacting requirements because the reference point in the calibrating configuration is subject to a displacement due to heating. These measurement errors can be prevented by a two point measurement of the workpiece. In a two point measurement the diameter of the workpiece can be determined directly.
The sensor contacts two diametrically opposite points on the workpiece directly and ascertains the appropriate dimension directly by numerical computation from the displacement of the carriage. A sensor for sensing the workpiece presence is known which can be mounted on a supporting arm. The supporting arm rests in a cradle-like recess of a carriage and can be pivoted into a working position for measuring the workpiece. Since the range of action of the sensor and support arm only extends approximately to the machine tool turning center, an absolute measurement of a workpiece diameter by the carriage system of the machine tool is possible only for workpieces of small diameter.